Ink ejection type writing unit

Claim 1

In an arrangement for applying liquid droplets to a surface comprising, a liquid-applying unit including a housing with a front wall facing a surface to which the unit is to apply a liquid, a chamber having an intake channel connected to a liquid supply container and a discharge channel in said front wall through which the liquid is discharged from the chamber into the atmosphere, pressure-producing means for producing short duration pressure increases in the liquid in the chamber, the chamber having means dividing the chamber into an outer chamber portion adjacent to the discharge channel and an inner chamber portion, a connecting channel in the dividing means connecting outer and inner chamber portions, the connecting channel being axially aligned with the discharge channel and the intake channel being in communication with the outer chamber portion, the inner chamber portion having a larger diameter portion in contact with the pressure-producing means and a smaller diameter portion adjacent to the connecting channel, the improvement comprising: means defining a first vent passageway for connecting the outer chamber portion to the atmosphere; means defining a second vent passageway connecting the larger diameter portion of said inner chamber portion to the atmosphere; first and second transparent tubes connected at one end to the first and second vent passageways, respectively, and extending outwardly of the liquid applying unit; and first and second closure means removably attached to the other end of the first and second tubes, respectively, so that bubbles in the liquid in the outer and inner chamber portions are collected in the tubes and visible from externally thereof.